Harmful alcohol use (heavy use, abuse, and dependence) in adulthood is a leading cause of morbidity and mortality in the US. Longitudinal data indicate that rates of heavy alcohol use, marijuana use, and daily smoking peak in the 20s and decline slowly thereafter. Rates of abuse and dependence on alcohol and illicit drugs follow a similar trend. However, there is a substantial portion of the population whose substance use persists or even escalates through young adulthood. Sustained alcohol, nicotine, and marijuana misuse can progress to dependence and contribute to failure to successfully adopt adult roles and to the emergence of social, health, and mental health problems. The proposed study uses data from the longitudinal International Youth Development Study (IYDS) to examine the persistence and desistence of alcohol use and related harms in adulthood. The current proposal seeks support to follow-up the Washington State (WA) IYDS cohort at ages 29 and 31 years. Support to follow up the Victoria, Australia (VIC) cohort is being provided separately. The IYDS is a gender-balanced, multiethnic, representative sample that used matched assessments and methods in the two states (WA and VIC). The panel of 1556 participants was previously interviewed 4 times at ages 13, 14, 15, (2002-04, funded by NIDA) and 25 (in 2014-15 with Australian research funding). Sample retention at age 25 was over 87% in both states. IYDS measures have been designed from a theoretically guided approach to identify varied patterns of substance use and risk and protective factors at the family, school, community, peer and individual levels. The study aims to: 1) compare patterns of persistence and desistence of alcohol use and related harms, 2) identify adolescent and concurrent adult risk and protective factors that predict alcohol use and related harms, and 3) pull together adolescent, young adult, and adult risk and protective factors into lifecourse mediational models. Cross-national comparisons are an integral part of all three aims. Understanding how adult influences lead to reductions in alcohol and other drug use is important in the current historical context where adult roles (e.g. marriage, child rearing, and education) are being progressively delayed. The proposed project will contribute to scientific understanding of modifiable factors that influence adult alcohol problems and will more precisely identify the processes that influence whether and why adults persist or desist in alcohol use and related harms during adulthood. The use of a cross-national design provides a unique and important opportunity for testing existing theories and prevention models of harmful alcohol use. Results will inform the development of effective prevention and treatment interventions aimed at reducing harmful adult alcohol use and related problem behaviors.